Imaging lens and imaging apparatus

ABSTRACT

An imaging lens is constituted by, in order from the object side to the image side: a first lens group; a stop; and a second lens group having a positive refractive power. The first lens group is constituted by, in order from the object side to the image side: a 1-1 negative meniscus lens having a concave surface toward the image side; a 1-2 negative meniscus lens having a concave surface toward the image side; a 1-3 biconcave lens; and a 1-4 positive lens. The second lens group is constituted by, in order from the object side to the image side: a 2A lens group having a positive refractive power; and a 2B lens group having a positive refractive power as a whole, constituted by a 2B-1 positive lens, a 2B-2 negative lens, and a 2B-3 positive lens. Predetermined conditional formulae are satisfied.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-021988 filed on Feb. 8, 2016. The above application is hereby expressly incorporated by reference, in its entirety, into the present application.

BACKGROUND

The present disclosure is related to an imaging lens which can be favorably utilized in a vehicle mounted camera, a surveillance camera, etc., and to an imaging apparatus equipped with this imaging lens.

Known imaging lenses for use in vehicle mounted cameras, surveillance cameras, etc. are disclosed in Japanese Unexamined Patent Publication Nos. 2013-148823, 2015-075533, and 2004-093593. Japanese Unexamined Patent Publication No. 2013-148823 discloses an imaging lens constituted by, in order from the object side to the image side, a front group, a stop, and a rear group.

SUMMARY

The lenses disclosed in Japanese Unexamined Patent Publication Nos. 2013-148823 and 2004-093593 do not sufficiently correct lateral chromatic aberration, and more favorable lenses are desired.

In addition, it is necessary for imaging lenses to be used in vehicle mounted cameras, surveillance cameras, etc. to image wide ranges. Therefore, there is demand for angles of view which are wide to a certain degree. However, the lenses disclosed in Japanese Unexamined Patent Publication No. 2015-075533 all have full angles of view of 90° or less, and lenses having wide angles of view are desired.

The present disclosure has been developed in view of the foregoing circumstances. The present disclosure provides an imaging lens having a wide angle of view that corrects various aberrations including lateral chromatic aberration, as well as an imaging apparatus equipped with the imaging lens.

An imaging lens of the present disclosure consists of, in order from the object side to the image side:

-   -   a first lens group;     -   a stop; and     -   a second lens group having a positive refractive power;     -   the first lens group consisting of, in order from the object         side to the image side:         -   a 1-1 negative meniscus lens having a concave surface toward             the image side;         -   a 1-2 negative meniscus lens having a concave surface toward             the image side;         -   a 1-3 biconcave lens; and         -   a 1-4 positive lens;     -   the second lens group consisting of, in order from the object         side to the image side:         -   a 2A lens group having a positive refractive power; and         -   a 2B lens group having a positive refractive power as a             whole, consisting of a 2B-1 positive lens, a 2B-2 negative             lens, and a 2B-3 positive lens; and

Conditional Formulae (1) and (2) below being satisfied. Note that it is preferable for Conditional Formulae (1-1) and/or (2-1) to be satisfied. 15<vd1<35  (1) 16<vd1<32  (1-1) −4.3<vd2BL2−vd1<10  (2) −3.8<vd2BL2−vd1<5  (2-1)

wherein vd1 is the Abbe's number of the 1-1 negative meniscus lens, and vd2BL2 is the Abbe's number of the 2B-2 negative lens.

In the imaging lens of the present disclosure, it is preferable for Conditional Formula (3) below to be satisfied, and more preferable for Conditional Formula (3-1) below to be satisfied. 0<vd4−vd1<30  (3) 5<vd4−vd1<28  (3-1)

wherein vd4 is the Abbe's number of the 1-4 positive lens and vd1 is the Abbe's number of the 1-1 negative meniscus lens.

In addition, in the imaging lens of the present disclosure, it is preferable for Conditional Formula (4) below to be satisfied, and more preferable for Conditional Formula (4-1) below to be satisfied. −0.015<θgF1−θgF2BL2<0.04  (4) −0.013<θgF1−θgF2BL2<0.03  (4-1)

wherein θgF1 is the partial dispersion ratio of the 1-1 negative meniscus lens, and θgF2BL2 is the partial dispersion ratio of the 2B-2 negative lens.

In addition, in the imaging lens of the present disclosure, it is preferable for Conditional Formula (5) below to be satisfied, and more preferable for Conditional Formula (5-1) below to be satisfied. 0<θgF1−θgF4<0.2  (5) 0.02<θgF1−θgF4<0.15  (5-1)

wherein θgF1 is the partial dispersion ratio of the 1-1 negative meniscus lens, and θgF4 is the partial dispersion ratio of the 1-4 positive lens.

In addition, in the imaging lens of the present disclosure, it is preferable for Conditional Formula (6) below to be satisfied, and more preferable for Conditional Formula (6-1) below to be satisfied. −0.5<f/fL1<−0.2  (6) −0 0.4<f/fL1<−0.25  (6-1)

wherein f is the focal length of the entire lens system, and fL1 is the focal length of the 1-1 negative meniscus lens.

In addition, in the imaging lens of the present disclosure, it is preferable for Conditional Formula (7) below to be satisfied, and more preferable for Conditional Formula (7-1) below to be satisfied. 0.5<f2B/f2A<2  (7) 0.7<f2B/f2A<1.6  (7-1)

wherein f2B is the focal length of the 2B lens group, and f2A is the focal length of the 2A lens group.

In addition, in the imaging lens of the present disclosure, it is preferable for Conditional Formula (8) below to be satisfied, and more preferable for Conditional Formula (8-1) below to be satisfied. −30<(vd1+vd2BL2)/2−vd4<0  (8) −25<(vd1+vd2BL2)/2−vd4<−5  (8-1)

wherein vd1 is the Abbe's number of the 1-1 negative meniscus lens, vd2BL2 is the Abbe's number of the 2B-2 negative lens, and vd4 is the Abbe's number of the 1-4 positive lens.

In addition, in the imaging lens of the present disclosure, it is preferable for Conditional Formula (9) below to be satisfied, and more preferable for Conditional Formula (9-1) below to be satisfied. 0<(θgF1+θgF2BL2)/2−θgF4<0.2  (9) 0.02<(θgF1+θgF2BL2)/2−θgF4<0.15  (9-1)

wherein θgF1 is the partial dispersion ratio of the 1-1 negative meniscus lens, θgF2BL2 is the partial dispersion ratio of the 2B-2 negative lens, and θgF4 is the partial dispersion ratio of the 1-4 positive lens.

In addition, it is preferable for the 2A lens group to consist of, in order from the object side to the image side, a 2A-1 positive lens, a 2A-2 negative lens, and a 2A-3 positive lens. In this case, it is preferable for the 2A-3 positive lens to be a positive lens having a convex surface toward the image side, and for the 2B-1 positive lens to be a positive lens having a convex surface toward the object side.

An imaging apparatus of the present disclosure is equipped with the imaging lens of the present disclosure.

Note that the above expression “consists of” means that lenses that practically have no power, optical elements other than lenses such as a stop, a cover glass, and filters, and mechanical components such as lens flanges, a lens barrel, an imaging element, a camera shake correcting mechanism, etc. may be included, in addition to the constituent elements listed above.

Note that the surface shapes, the radii of curvature, and/or the signs of the refractive powers of lenses in the above lens are those which are considered in the paraxial region for lenses that include aspherical surfaces. In addition, all of the above conditional formulae are those which employ the d line (wavelength: 587.6 nm) as a standard. In addition, the partial dispersion ratio (θgF) is represented by the formula below. θgF=(ng−nF)/(nF−nC)

wherein ng is the refractive index with respect to the g line, nF is the refractive index with respect to the F line, and nC is the refractive index with respect to the C line.

The imaging lens of the present disclosure consists of, in order from the object side to the image side: the first lens group; the stop; and the second lens group having a positive refractive power. The first lens group consists of, in order from the object side to the image side: the 1-1 negative meniscus lens having a concave surface toward the image side; the 1-2 negative meniscus lens having a concave surface toward the image side; the 1-3 biconcave lens; and the 1-4 positive lens. The second lens group consists of, in order from the object side to the image side: the 2A lens group having a positive refractive power; and the 2B lens group having a positive refractive power as a whole, consisting of the 2B-1 positive lens, the 2B-2 negative lens, and the 2B-3 positive lens. In addition, Conditional Formulae (1) and (2) below are satisfied. Therefore, it is possible for the imaging lens to have a wide angle of view and favorably correct various aberrations including lateral chromatic aberration. 15<vd1<35  (1) −4.3<vd2BL2−vd1<10  (2)

In addition, the imaging apparatus of the present disclosure is equipped with the imaging lens of the present disclosure. Therefore, the imaging apparatus has a wide angle of view and is capable of obtaining images having high image quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a collection of sectional diagrams that illustrate the lens configuration of an imaging lens according to an embodiment of the present disclosure (common with Example 1).

FIG. 2 is a cross sectional diagram that illustrates the lens configuration of an imaging lens according to Example 2 of the present disclosure.

FIG. 3 is a cross sectional diagram that illustrates the lens configuration of an imaging lens according to Example 3 of the present disclosure.

FIG. 4 is a cross sectional diagram that illustrates the lens configuration of an imaging lens according to Example 4 of the present disclosure.

FIG. 5 is a collection of diagrams that illustrate aberrations of the imaging lens according to Example 1.

FIG. 6 is a collection of diagrams that illustrate aberrations of the imaging lens according to Example 2.

FIG. 7 is a collection of diagrams that illustrate aberrations of the imaging lens according to Example 3.

FIG. 8 is a collection of diagrams that illustrate aberrations of the imaging lens according to Example 4.

FIG. 9 is a schematic diagram of an imaging apparatus according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings. FIG. 1 is a cross sectional diagram that illustrates the lens configuration of an imaging lens according to an embodiment of the present disclosure. The example of the configuration illustrated in FIG. 1 corresponds to the configuration of an imaging lens of Example 1 to be described later. In FIG. 1, the left side is the object side, and the right side is the image side. The aperture stop St illustrated in FIG. 1 does not necessarily represent the size and/or the shape thereof, but the position of the stop along an optical axis Z. In addition, FIG. 1 also illustrates the optical paths of an axial light beam wa and a light beam wb at a maximum angle of view.

As illustrated in FIG. 1, the imaging lens 1 is constituted by, in order from the object side to the image side, a first lens group G1, the aperture stop St, and a second lens group G2 having a positive refractive power. The incident angle of off axis light beams with respect to an image formation plane Sim can be suppressed, by adopting such a configuration.

The first lens group G1 is constituted by, in order from the object side to the image side: a 1-1 negative meniscus lens L11 having a concave surface toward the image side, a 1-2 negative meniscus lens L11 having a concave surface toward the image side, a 1-3 biconcave lens L13, and a 1-4 positive lens L14.

By positioning the 1-1 negative meniscus lens L11 most toward the object side, the angle of off axis light rays that enter the lens groups more toward the image side than the 1-1 negative meniscus lens L11 can be reduced. In addition, the negative meniscus shape having the concave surface toward the image side can suppress the generation of distortion. Further, two negative meniscus lenses, the 1-1 negative meniscus lens L11 and the 1-2 negative meniscus lens L12, are provided consecutively. Such a configuration is more advantageous from the viewpoint of correcting distortion. Note that there is a tendency for the radii of negative meniscus lenses to increase if three or more negative meniscus lenses are provided consecutively. Therefore, it is advantageous to maintain the number of negative meniscus lenses to two or fewer, from the viewpoint of decreasing the radius of the lens.

In addition, a positive lens is not positioned between the 1-2 negative meniscus lens L12 and the 1-3 biconcave lens L13. Therefore, it is not necessary to impart excessively strong refractive powers to the negative meniscus lenses. As a result, the generation of off axis higher order aberrations can be suppressed, and this configuration is also advantageous from the viewpoint of widening the angle of view.

In addition, the 1-3 biconcave lens L13 exhibits the effects of suppressing the generation of excessively corrected spherical aberration and imparting negative refractive power. Such a configuration is advantageous from the viewpoints of widening the angle of view and securing back focus.

In addition, the 1-4 positive lens L14 exhibits the effects of correcting distortion and lateral chromatic aberration, while decreasing the incident angles of marginal axial light rays that enter the second lens group G2 , to suppress the generation of spherical aberration.

The second lens group G2 is constituted by, in order from the object side to the image side, a 2A lens group G2A having a positive refractive power, and a 2B lens group having a positive refractive power as a whole, consisting of a 2B-1 positive lens L24, a 2B-2 negative lens L25, and a 2B-3 positive lens L26.

By dividing the second lens group G2 into two lens groups having positive refractive powers, which are the 2A lens group G2A and the 2B lens group G2B, the generation of spherical aberration can be suppressed.

In addition, by the 2B lens group G2B being of a three lens configuration constituted by the 2B-1 positive lens L24, the 2B-2 negative lens L25, and the 2B-3 positive lens L26, various aberrations which are generated within the 2B lens group G2B, such as longitudinal chromatic aberration, lateral chromatic aberration, spherical aberration, and astigmatism, can be favorably corrected.

Further, the imaging lens is configured such that Conditional Formulae (1) and (2) below are satisfied. 15<vd1<35  (1) 16<vd1<32  (1-1) −4.3<vd2BL2−vd1<10  (2) −3.8<vd2BL2−vd1<5  (2-1)

wherein vd1 is the Abbe's number of the 1-1 negative meniscus lens, and vd2BL2 is the Abbe's number of the 2B-2 negative lens.

By configuring the imaging lens such that the value of vd1 is not less than or equal to the lower limit defined in Conditional Formula (1), lateral chromatic aberration can be corrected appropriately. By configuring the imaging lens such that the value of vd1 is not greater than or equal to the upper limit defined in Conditional Formula (1), a material having a large partial dispersion ratio can be selected, and therefore second order lateral chromatic aberration can be corrected appropriately. Note that more favorable properties can be obtained if Conditional Formula (1-1) is satisfied.

In addition, by Conditional Formula (2) being satisfied, lateral chromatic aberration can be corrected appropriately. Note that more favorable properties can be obtained if Conditional Formula (2-1) is satisfied.

It is preferable for Conditional Formula (3) to be satisfied in the imaging lens of the present disclosure. By configuring the imaging lens such that the value of vd4−vd1 is not less than or equal to the lower limit defined in Conditional Formula (3), second order lateral chromatic aberration can be corrected appropriately. By configuring the imaging lens such that the value of vd4−vd1 is not greater than or equal to the upper limit defined in Conditional Formula (3), first order lateral chromatic aberration can be corrected appropriately. Note that more favorable properties can be obtained if Conditional Formula (3-1) is satisfied. 0<vd4−vd1<30  (3) 5<vd4−vd1<28  (3-1)

wherein vd4 is the Abbe's number of the 1-4 positive lens and vd1 is the Abbe's number of the 1-1 negative meniscus lens.

In addition, it is preferable for Conditional Formula (4) below to be satisfied, By Conditional Formula (4) being satisfied, second order lateral chromatic aberration can be corrected appropriately. Note that more favorable properties can be obtained if Conditional Formula (4-1) is satisfied. −0.015<θgF1−θgF2BL2<0.04  (4) −0.013<θgF1−θgF2BL2<0.03  (4-1)

wherein θgF1 is the partial dispersion ratio of the 1-1 negative meniscus lens, and θgF2BL2 is the partial dispersion ratio of the 2B-2 negative lens.

In addition, it is preferable for Conditional Formula (5) below to be satisfied. By Conditional Formula (5) being satisfied, second order lateral chromatic aberration can be corrected appropriately. Note that more favorable properties can be obtained if Conditional Formula (5-1) is satisfied. 0<θgF1−θgF4<0.2  (5) 0.02<θgF1−θgF4<0.15  (5-1)

wherein θgF1 is the partial dispersion ratio of the 1-1 negative meniscus lens, and θgF4 is the partial dispersion ratio of the 1-4 positive lens.

In addition, it is preferable for Conditional Formula (6) below to be satisfied. By Conditional Formula (6) being satisfied, the advantageous effects related to Conditional Formula (1) will be exhibited more effectively. Note that more favorable properties can be obtained if Conditional Formula (6-1) is satisfied. −0.5<f/fL1<−0.2  (6) −0.4<f/fL1<−0.25  (6-1)

wherein f is the focal length of the entire lens system, and fL1 is the focal length of the 1-1 negative meniscus lens.

In addition, it is preferable for Conditional Formula (7) below to be satisfied. By configuring the imaging lens such that the value of f2B/f2A is not less than or equal to the lower limit defined in Conditional Formula (7), positive refractive power is appropriately distributed between the 2A lens group G2A and the 2B lens group G2B. As a result, the generation of spherical aberration and astigmatism can be suppressed. By configuring the imaging lens such that the value of f2B/f2A is not greater than or equal to the upper limit defined in Conditional Formula (7), the incident angle of off axis light rays with respect to the image formation plane Sim can be suppressed. Note that more favorable properties can be obtained if Conditional Formula (7-1) is satisfied. 0.5<f2B/f2A<2  (7) 0.7<f2B/f2A<1.6  (7-1)

wherein f2B is the focal length of the 2B lens group, and f2A is the focal length of the 2A lens group.

In addition, it is preferable for Conditional Formula (8) below to be satisfied, By Conditional Formula (8) being satisfied, second order lateral chromatic aberration can be corrected appropriately. Note that more favorable properties can be obtained if Conditional Formula (8-1) is satisfied. −30<(vd1+vd2BL2)/2−vd4<0  (8) −25<(vd1+vd2BL2)/2−vd4<−5  (8-1)

wherein vd1 is the Abbe's number of the 1-1 negative meniscus lens, vd2BL2 is the Abbe's number of the 2B-2 negative lens, and vd4 is the Abbe's number of the 1-4 positive lens.

In addition, it is preferable for Conditional Formula (9) below to be satisfied, By Conditional Formula (9) being satisfied, second order lateral chromatic aberration can be corrected appropriately. Note that more favorable properties can be obtained if Conditional Formula (9-1) is satisfied. 0<(θgF1+θgF2BL2)/2−θgF4<0.2  (9) 0.02<(θgF1+θgF2BL2)/2−θgF4<0.15  (9-1)

wherein θgF1 is the partial dispersion ratio of the 1-1 negative meniscus lens, θgF2BL2 is the partial dispersion ratio of the 2B-2 negative lens, and θgF4 is the partial dispersion ratio of the 1-4 positive lens.

In addition, it is preferable for the 2A lens group to consist of, in order from the object side to the image side, a 2A-1 positive lens L21, a 2A-2 negative lens L22, and a 2A-3 positive lens L23. By adopting this configuration, longitudinal chromatic aberration, various aberrations which are generated within the 2A lens group G2A, such as longitudinal chromatic aberration, lateral chromatic aberration, spherical aberration, and astigmatism, can be favorably corrected.

In the case that the 2A lens group G2A is of the configuration described above, it is preferable for the 2A-3 positive lens L23 to be a positive lens having a convex surface toward the image side, and for the 2B-1 positive lens L24 to be a positive lens having a convex surface toward the object side. In this manner, by an air lens between the 2A-3 positive lens L23 and the 2B-1 positive lens L24 having positive refractive power and by the surface toward the object side of the 2B-1 positive lens L24 being a convex surface, the heights of light rays at peripheral angles of view that enter the 2B-1 positive lens L24 will increase, and the influence of positive refractive power will become stronger. As a result, the angles at which light rays at peripheral angles of view enter the image formation plane Sim can be decreased.

In addition, in the case that the 2A lens group G2A is of the configuration described above, it is preferable for the 2A-2 negative lens L22 and the 2A-3 positive lens L23 to be cemented together, and for the shape of the coupling surface between the two to be convex toward the object side. This configuration enables the generation of astigmatism to be suppressed and is advantageous from the viewpoint of correcting lateral chromatic aberration.

In addition, it is preferable for the 2B-2 negative lens L25 and the 2B-3 positive lens L26 to be cemented together, and for the shape of the coupling surface between the two to be convex toward the object side. This configuration enables the generation of astigmatism to be suppressed and is advantageous from the viewpoint of correcting lateral chromatic aberration.

In addition, it is preferable for Conditional Formula (10) below to be satisfied. By configuring the imaging lens such that the value of β2B is not less than or equal to the lower limit defined in Conditional Formula (10), and by the transverse magnification of the 2B lens group G2B being a positive magnification, the burden of the 2B lens group G2B with respect to bearing refractive power can be decreased, and therefore the generation of spherical aberration at the 2B lens group G2B can be suppressed. In addition, the 2B lens group G2B is further from the aperture stop St than the 2A lens group G2A, and the heights of off axis light rays that enter the 2B lens group G2B are higher. Therefore, various off axis aberrations can be controlled during design of the imaging lens. At this time, that the burden of spherical aberration is small means that achieving balance between off axis and axial aberrations is facilitated. By configuring the imaging lens such that the value of β2B is not greater than or equal to the upper limit defined in Conditional Formula (10), the burden of the 2A lens group G2A with respect to bearing refractive power can be decreased, and therefore the generation of spherical aberration can be suppressed. Note that more favorable properties can be obtained if Conditional Formula (10-1) is satisfied. 0<β2B<0.95  (10) 0.2<β2B<0.8  (10-1)

wherein β2B is the transverse magnification of the 2B lens group.

In addition, it is preferable for Conditional Formula (11) below to be satisfied. By configuring the imaging lens such that the value of f2/f1 is not less than or equal to the lower limit defined in Conditional Formula (11), the generation of spherical aberration at the second lens group G2 can be suppressed. Configuring the imaging lens such that the value of f2/f1 is not greater than or equal to the upper limit defined in Conditional Formula (11) is advantageous from the viewpoint of widening the angle of view, and also enables back focus to be secured. Note that more favorable properties can be obtained if Conditional Formula (11-1) is satisfied. −1<f2/f1<0.5  (11) −0.5<f2/f1<0.3  (11-1)

wherein f2 is the focal length of the second lens group, and f1 is the focal length of the first lens group.

In addition, it is preferable for Conditional Formula (12) below to be satisfied. By configuring the imaging lens such that the value of (2BL1f+2AL3r)/(2BL1f−2AL3r) is not less than or equal to the lower limit defined in Conditional Formula (12), the generation of astigmatism and distortion can be suppressed. By configuring the imaging lens such that the value of (2BL1f+2AL3r)/(2BL1f−2AL3r) is not greater than or equal to the upper limit defined in Conditional Formula (12), the incident angles of off axis light rays with respect to the image formation plane Sim can be suppressed. Note that more favorable properties can be obtained if Conditional Formula (12-1) is satisfied. 0<(2BL1f+2AL3r)/(2BL1f−2AL3r)<0.5  (12) 0<(2BL1f+2AL3r)/(2BL1f−2AL3r)<0.4  (12-1)

wherein 2BL1 f is the radius of curvature of the surface toward the object side of the 2B-1 positive lens, and 2AL3r is the radius of curvature of the surface toward the image side of the 2A-3 positive lens.

It is preferable for a protective multiple layer film coating to be administered in the case that the present imaging lens is to be utilized in extreme environments. Further, an antireflection coating may be administered in addition to the protective coating, in order to reduce ghost light and the like during utilization of the imaging lens.

In addition, in the case that this imaging lens is applied to an imaging apparatus, a cover glass, prisms, and/or various filters, such as an infrared cutoff filter and a low pass filter, may be provided between the lens system and the image formation plane Sim, depending on the configuration of the imaging apparatus. Note that these filters may be provided among the lenses instead of being provided between the lens system and the image formation plane Sim. As a further alternative, coatings that exhibit the same effects as these filters may be administered on the lens surfaces of the lenses.

Next, examples of numerical values of the imaging lens of the present disclosure will be described.

First, an imaging lens of Example 1 will be described. FIG. 1 is a cross sectional diagram that illustrates the lens configuration of the imaging lens of Example 1. Note that in FIG. 1 and FIGS. 2 through 4 that correspond to Examples 2 through 4 to be described later, the left side is the object side, the right side is the image side, and the aperture stops St illustrated therein do not necessarily represent the sizes and shapes thereof but only the positions thereof along the optical axis Z.

Basic lens data are shown in Table 1, data related to various items are shown in Table 2, and data related to aspherical surface coefficients are shown in Table 3 for the imaging lens of Example 1. The meanings of the symbols in the tables will be described below with those for Example 1 as an example. However, the meanings of the symbols are basically the same for Examples 2 through 4.

In the lens data of Table 1, surface numbers that sequentially increase from the object side to the image side, with the surface toward the object side of the constituent element at the most object side designated as first, are shown in the column Surface Number. The radii of curvature of each surface are shown in the column Radius of Curvature. The distances between each surface and a next surface are shown in the column Distance. The refractive indices with respect to the d line (wavelength: 587.6 nm) of each optical element are shown in the column nd. The Abbe's numbers with respect to the d line (wavelength: 587.6 nm) of each optical element are shown in the column vd. The partial dispersion ratios of each optical element are shown in the column θgF.

Here, the signs of the radii of curvature are positive in cases that the surface shape is convex toward the object side, and negative in cases that the surface shape is convex toward the image side. Table 1 also shows data regarding the aperture stop St. Text reading “(St)” is indicated along with a surface number in the column of the surface number at the surface corresponding to the aperture stop.

The values of the focal length f′ of the entire lens system, the back focus Bf′, the F number F No., and the full angle of view 2ω are shown as data related to various items in Table 2.

In the data shown in each of the tables below, degrees are used as the units for angles and mm are used as the units for lengths. However, it is possible for optical systems to be proportionately enlarged or proportionately reduced and utilized. Therefore, other appropriate units may be used.

In the lens data of Table 1, the surface numbers of aspherical surfaces are appended with the mark “*”, and numerical values that represent paraxial radii of curvature are shown as the radii of curvature of the aspherical surfaces. Table 3 shows aspherical surface coefficients related to these aspherical surfaces. In Table 3, “E±n” (n is an integer) means that the numerical values are multiplied by 10^(±n). The aspherical surface coefficients are the values of the coefficients KA and Am (m=3 . . . 12) in the aspherical surface formula below.

${Zd} = {\frac{C \times h^{2}}{1 + \sqrt{1 - {{KA} \times C^{2} \times h^{2}}}} + {\sum\limits_{m}{{Am} \times h^{m}}}}$

wherein Zd is the depth of the aspherical surface (the length of a normal line that extends from a point on the aspherical surface at a height h to a plane perpendicular to the optical axis that contacts the apex of the aspherical surface), h is the height (the distance from the optical axis), C is the inverse of the paraxial radius of curvature, and KA and Am are aspherical surface coefficients (m=3 . . . 12).

TABLE 1 Example 1: Lens Data Radius of Surface Number Curvature Distance nd νd θgF 1 10.31915 1.014 1.80000 29.84 0.60178 2 3.43524 1.021 *3 25.24978 0.563 1.53112 55.30 0.55145 *4 3.82209 2.704 5 −10.25368 1.012 1.59282 68.62 0.54414 6 4.58845 0.210 7 5.36646 2.254 1.88300 40.76 0.56679 8 −8.53492 2.270 9 (stop) ∞ 0.225 *10 10.97865 0.916 1.53112 55.30 0.55145 *11 −5.47894 0.225 12 −8.03099 0.563 1.78590 44.20 0.56317 13 3.84304 2.126 1.49700 81.54 0.53748 14 −4.84976 0.225 *15 6.43949 2.065 1.53112 55.30 0.55145 *16 −3.92986 0.225 17 −5.32161 0.563 1.80000 29.84 0.60178 18 5.28788 2.451 1.49700 81.54 0.53748 19 −5.60671 3.023

TABLE 2 Example 1: Items f′ 2.430 Bf′ 3.023 FNo. 2.30 2ω[°] 111.8

TABLE 3 Example 1: Aspherical Surface Coefficients Surface Number 3 4 10 KA 1.0000000E+00 −4.3860663E+00  1.0000000E+00 A3 −7.0382068E−18   1.2512899E−03 −3.5177231E−17 A4 6.1765716E−02  7.0338531E−02 −8.3851595E−03 A5 −2.0476378E−02  −3.0487073E−03 −5.0920775E−03 A6 −3.6519374E−03  −1.7029685E−02  4.3764741E−03 A7 3.1888905E−03  4.3068658E−03 −5.0265478E−03 A8 3.2819210E−05  2.9871340E−03  1.2901144E−03 A9 −2.9161972E−04  −1.4216292E−03  1.7460366E−03 A10 1.7530083E−05 −8.7630654E−05 −2.5098175E−03 A11 1.4865165E−05  1.1415871E−04  1.3113798E−03 A12 −2.2030589E−06  −1.3417545E−05 −3.1087869E−04 Surface Number 11 15 16 KA  1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 −2.7632266E−17 0.0000000E+00 1.7062371E−17 A4 −1.0809975E−02 −4.1927970E−03  2.3965961E−03 A5  1.5256061E−03 1.5708422E−03 −2.0383009E−03  A6 −5.2126009E−03 2.5589142E−04 5.3798824E−03 A7  1.3276128E−03 −1.9833597E−03  −5.3673251E−03  A8  4.3651101E−03 1.4164491E−03 1.8444177E−03 A9 −5.5600472E−03 −2.2630085E−04  4.2530995E−04 A10  2.1673942E−03 −1.5924379E−04  −5.3836422E−04  A11 −5.7076089E−05 7.6343519E−05 1.5923857E−04 A12 −1.2088863E−04 −9.7691800E−06  −1.6377765E−05 

FIG. 5 is a collection of diagrams that illustrate various aberrations of the imaging lens of Example 1. Note that in FIG. 5, diagrams that illustrate spherical aberration, astigmatism, distortion, and lateral chromatic aberration are illustrated in this order from the left side of the drawing sheet. These aberration diagrams illustrate aberrations in a state when the object distance is infinity. The diagram that illustrates spherical aberration shows aberrations related to the d line (wavelength: 587.6 nm), the C line (wavelength: 656.3 nm), the F line (wavelength: 486.1 nm), and the g line (wavelength: 435.8 nm) as a solid line, a long broken line, a short broken line, and a gray solid line, respectively. In the diagram that illustrates astigmatism, aberrations in the sagittal direction and aberrations in the tangential direction are indicated by a solid line and a dotted line, respectively. In the diagram that illustrates lateral chromatic diagram, aberrations related to the C line (wavelength: 656.3 nm), the F line (wavelength: 486.1 nm), and the g line (wavelength: 435.8 nm) are shown as a long broken line, a dotted line, and a gray solid line, respectively. In the diagram that illustrates spherical aberration, “FNo.” denotes the F number. In the other diagrams that illustrate the aberrations, ω denotes half angles of view.

The symbols, the meanings, and the manners in which the various pieces of data are described in the description of Example 1 above are the same for the examples to be described below unless otherwise noted. Therefore, redundant descriptions will be omitted hereinafter.

Next, an imaging lens of Example 2 will be described. FIG. 2 is a cross sectional diagram that illustrates the lens configuration of the imaging lens of Example 2. Basic lens data are shown in Table 4, data related to various items are shown in Table 5, and aspherical surface coefficients are shown in Table 6 for the imaging lens of Example 2. In addition, FIG. 6 is a collection of diagrams that illustrate various aberrations of the imaging lens of Example 2.

TABLE 4 Example 2: Lens Data Radius of Surface Number Curvature Distance nd νd θgF 1 8.22774 1.014 1.85896 22.73 0.62844 2 3.43523 1.299 *3 56.33933 0.563 1.53112 55.30 0.55145 *4 3.68222 2.681 5 −8.65462 1.014 1.59282 68.62 0.54414 6 4.53857 0.198 7 5.34112 2.253 1.88300 40.76 0.56679 8 −7.29460 2.065 9 (stop) ∞ 0.225 *10 11.65462 0.944 1.53112 55.30 0.55145 *11 −5.03343 0.225 12 −7.69182 0.563 1.80400 46.58 0.55730 13 4.08659 1.942 1.49700 81.54 0.53748 14 −5.33616 0.225 *15 7.24245 1.930 1.53112 55.30 0.55145 *16 −3.95944 0.225 17 −5.93963 0.563 1.80518 25.42 0.61616 18 5.27620 2.631 1.49700 81.54 0.53748 19 −5.17653 3.020

TABLE 5 Example 2: Items f′ 2.436 Bf′ 3.020 FNo. 2.31 2ω[°] 111.8

TABLE 6 Example 2: Aspherical Surface Coefficients Surface Number 3 4 10 KA 1.0000000E+00 −5.1426999E+00  1.0000000E+00 A3 1.4076414E−17 1.7898935E−03 6.3958602E−18 A4 6.8384507E−02 7.9231683E−02 −8.2343640E−03  A5 −2.4756423E−02  2.8191193E−04 −4.2078871E−03  A6 −3.8784148E−03  −2.3739399E−02  2.6042175E−03 A7 3.9267631E−03 5.7572350E−03 −4.8755531E−03  A8 −6.0952071E−05  4.2939468E−03 2.5007783E−03 A9 −3.4957650E−04  −1.8832211E−03  1.5703911E−03 A10 2.9048234E−05 −1.6475827E−04  −2.8839115E−03  A11 1.6524702E−05 1.4435406E−04 1.3431348E−03 A12 −2.6071062E−06  −1.3417545E−05  −2.6297060E−04  Surface Number 11 15 16 KA 1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 3.8748695E−17 0.0000000E+00 8.5311857E−18 A4 −1.0535719E−02  −5.0209177E−03  2.3305948E−03 A5 4.8814594E−04 3.7504038E−04 −2.9368184E−03  A6 −4.3441051E−03  1.0393155E−03 5.5596199E−03 A7 1.1291648E−03 −1.9725110E−03  −5.0791019E−03  A8 4.3972373E−03 1.2339111E−03 1.7373426E−03 A9 −5.3191929E−03  −1.9846840E−04  3.7868812E−04 A10 2.0109729E−03 −1.4303224E−04  −5.1821108E−04  A11 −9.1331624E−05  7.3743649E−05 1.6175624E−04 A12 −9.2125259E−05  −1.0321926E−05  −1.7709856E−05 

Next, an imaging lens of Example 3 will be described. FIG. 3 is a cross sectional diagram that illustrates the lens configuration of the imaging lens of Example 3. Basic lens data are shown in Table 7, data related to various items are shown in Table 8, and aspherical surface coefficients are shown in Table 9 for the imaging lens of Example 3. In addition, FIG. 7 is a collection of diagrams that illustrate various aberrations of the imaging lens of Example 3.

TABLE 7 Example 3: Lens Data Radius of Surface Number Curvature Distance nd νd θgF 1 6.55872 0.676 1.95906 17.47 0.65993 2 3.43525 1.258 *3 56.34361 0.563 1.53112 55.30 0.55145 *4 3.68220 2.697 5 −8.38112 1.014 1.59282 68.62 0.54414 6 3.88057 0.291 7 4.75732 2.187 1.88300 40.76 0.56679 8 −7.43526 1.466 9 (stop) ∞ 0.225 *10 16.05518 0.901 1.53112 55.30 0.55145 *11 −4.71312 0.225 12 −6.10781 0.580 1.72916 54.68 0.54451 13 3.56924 2.157 1.49700 81.54 0.53748 14 −5.10920 0.225 *15 6.34282 2.007 1.53112 55.30 0.55145 *16 −3.91665 0.225 17 −6.02267 0.563 1.89286 20.36 0.63944 18 6.43128 2.359 1.49700 81.54 0.53748 19 −5.17001 3.005

TABLE 8 Example 3: Items f′ 2.425 Bf′ 3.005 FNo. 2.31 2ω[°] 112.0

TABLE 9 Example 3: Aspherical Surface Coefficients Surface Number 3 4 10 KA 1.0000000E+00 −5.1426957E+00  1.0000000E+00 A3 0.0000000E+00 1.8679010E−03 3.1979301E−17 A4 6.8622883E−02 7.9256994E−02 −7.7359788E−03  A5 −2.5046668E−02  1.4390872E−03 −6.8594487E−03  A6 −3.9967733E−03  −2.4325185E−02  2.7929455E−03 A7 4.0062857E−03 5.4112362E−03 −3.6218995E−03  A8 −5.3850326E−05  4.4424823E−03 2.3109076E−03 A9 −3.5599887E−04  −1.7945312E−03  1.1385312E−03 A10 3.0179130E−05 −1.7467051E−04  −2.8170239E−03  A11 1.6710953E−05 1.3664239E−04 1.3900346E−03 A12 −2.6889001E−06  −1.3417545E−05  −2.8346564E−04  Surface Number 11 15 16 KA  1.0000000E+00 1.0000000E+00 1.0000000E+00 A3 −3.3666899E−17 4.2655928E−18 8.5311857E−18 A4 −9.6445245E−03 −4.6116698E−03  3.6555112E−03 A5 −2.7623004E−03 2.2007678E−04 −3.5715180E−03  A6 −3.2622984E−03 1.0562675E−03 5.4521856E−03 A7  2.5480347E−03 −1.8206695E−03  −4.7621299E−03  A8  3.6519960E−03 1.1842120E−03 1.6920898E−03 A9 −5.6724128E−03 −2.2481451E−04  3.3052739E−04 A10  2.2116376E−03 −1.3035129E−04  −5.0542219E−04  A11 −6.1312055E−05 7.5241995E−05 1.6432460E−04 A12 −1.1695468E−04 −1.1227970E−05  −1.8554583E−05 

Next, an imaging lens of Example 4 will be described. FIG. 4 is a cross sectional diagram that illustrates the lens configuration of the imaging lens of Example 4. Basic lens data are shown in Table 10, data related to various items are shown in Table 11, and aspherical surface coefficients are shown in Table 12 for the imaging lens of Example 3. In addition, FIG. 8 is a collection of diagrams that illustrate various aberrations of the imaging lens of Example 4.

TABLE 10 Example 4: Lens Data Radius of Surface Number Curvature Distance nd νd θgF 1 9.58990 1.014 1.80000 29.84 0.60178 2 3.43523 0.901 *3 22.13665 0.563 1.53112 55.30 0.55145 *4 3.92328 2.697 5 −10.55760 0.676 1.59282 68.62 0.54414 6 4.47980 0.354 7 5.65265 2.254 1.88300 40.76 0.56679 8 −8.84809 2.335 9 (stop) ∞ 0.225 *10 12.32374 0.923 1.53112 55.30 0.55145 *11 −4.82235 0.225 12 −8.60787 0.563 1.80400 46.58 0.55730 13 4.06367 2.159 1.49700 81.54 0.53748 14 −4.33714 0.225 *15 9.33876 1.679 1.53112 55.30 0.55145 *16 −4.80008 0.225 17 −6.28050 0.563 1.78470 26.29 0.61360 18 7.54633 2.087 1.49700 81.54 0.53748 19 −6.00170 3.369

TABLE 11 Example 4: Items f′ 2.421 Bf′ 3.369 FNo. 2.30 2ω[°] 112.0

TABLE 12 Example 4: Aspherical Surface Coefficients Surface Number 3 4 10 KA 1.0000000E+00 −4.8400882E+00  1.0000000E+00 A3 7.8080107E−18  1.4355447E−03  1.7738518E−17 A4 6.2084950E−02  7.0875828E−02 −7.1008779E−03 A5 −2.0852102E−02  −3.3098450E−03 −1.0008876E−02 A6 −3.4872424E−03  −1.7685507E−02  8.4161945E−03 A7 3.2684858E−03  4.7581531E−03 −4.1902447E−03 A8 1.3933303E−05  3.1368468E−03 −1.3764299E−03 A9 −2.9704765E−04  −1.5125208E−03  1.8155220E−03 A10 1.8415046E−05 −9.6980978E−05 −1.7262444E−03 A11 1.4988031E−05  1.1927349E−04  1.2662061E−03 A12 −2.2280805E−06  −1.3417545E−05 −4.2174287E−04 Surface Number 11 15 16 KA 1.0000000E+00  1.0000000E+00 1.0000000E+00 A3 7.0470218E−18 −4.7321421E−18 1.8928568E−17 A4 −7.8087995E−03  −4.5983881E−03 4.9204708E−04 A5 −1.5389961E−03   1.0858647E−03 −3.1187477E−03  A6 −5.1003425E−03   5.0603493E−04 6.0074345E−03 A7 4.3172143E−03 −2.1749280E−03 −5.5116607E−03  A8 2.7710593E−03  1.3955184E−03 1.7483359E−03 A9 −6.6192668E−03  −1.8376374E−04 4.6890997E−04 A10 2.9163806E−03 −1.6798470E−04 −5.3821675E−04  A11 5.5102849E−05  7.3550751E−05 1.5614444E−04 A12 −2.2836050E−04  −8.8871992E−06 −1.6020649E−05 

Table 13 shows values related to Conditional Formulae (1) through (12) for the imaging lenses of Examples 1 through 4. Note that all of the Examples employ the d line as a reference wavelength, and the values shown in Table 13 below are those for the reference wavelength.

TABLE 13 Formula Condition Example 1 Example 2 Example 3 Example 4 (1) νd1 29.84 22.73 17.47 29.84 (2) νd2BL2 − νd1 0.00 2.70 2.89 −3.55 (3) νd4 − νd1 10.92 18.04 23.29 10.92 (4) θgF1 − θgF2BL2 0.0000 0.0123 0.0205 −0.0118 (5) θgF1 − θgF4 0.0350 0.0616 0.0931 0.0350 (6) f/fL1 −0.353 −0.320 −0.288 −0.335 (7) f2B/f2A 1.239 1.517 1.592 0.862 (8) (νd1 + νd2BL2)/2 − νd4 −10.92 −16.69 −21.85 −12.70 (9) (θgF1 + θgF2BL2)/2 − θgF4 0.0350 0.0555 0.0829 0.0409 (10)  β2B 0.478 0.472 0.465 0.577 (11)  f2/f1 −0.118 0.058 0.154 −0.186 (12)  (2BL1f + 2AL3r)/(2BL1f − 2AL3r) 0.141 0.152 0.108 0.366

From the data above, it can be understood that all of the imaging lenses of Examples 1 through 4 satisfy Conditional Formulae (1) through (12), have wide full angles of view 2ω of 100° or greater, and are imaging lenses in which various aberrations including lateral chromatic aberration are favorably corrected.

Next, an imaging apparatus according to an embodiment of the present disclosure will be described. Here, an example in which the embodiment of the imaging apparatus of the present disclosure is applied to vehicle mounted cameras will be described. FIG. 9 illustrates the manner in which vehicle mounted cameras are mounted on an automobile.

In FIG. 9, an automobile 100 is equipped with an externally mounted camera 101 for imaging a blind spot range at the side surface on the side of the passenger seat, an externally mounted camera 102 for imaging a blind spot range at the rear side of the automobile 100, and a internally mounted camera which is mounted on the back surface of the rear view mirror and images the same range as the field of view of a driver. The externally mounted camera 101, the externally mounted camera 102, and the internally mounted camera 103 are imaging apparatuses which are equipped with imaging lenses according to an embodiment of the present disclosure and imaging elements that convert optical images formed by the imaging lenses into electrical signals. The vehicle mounted cameras of the present embodiment (the externally mounted camera 101, the externally mounted camera 102, and the internally mounted camera 103) are equipped with imaging lenses according to the embodiment of the present disclosure. Therefore, the imaging apparatuses are capable of obtaining images having wide angles of view and high image quality.

The present disclosure has been described with reference to the embodiments and Examples. However, the present disclosure is not limited to the above embodiments and Examples, and various modifications are possible. For example, the values of the radii of curvature, the surface distances, the refractive indices, the Abbe's numbers, the aspherical surface coefficients, etc. of each of the lenses are not limited to those exemplified in the above Examples, and may be different values.

In addition, the imaging apparatus according to embodiments of the present disclosure are not limited to vehicle mounted cameras. The imaging apparatus of the present disclosure may be a camera for a portable terminal, a surveillance camera, a digital camera, etc. 

What is claimed is:
 1. An imaging lens consisting of, in order from the object side to the image side: a first lens group; a stop; and a second lens group having a positive refractive power; the first lens group consisting of, in order from the object side to the image side: a first lens negative meniscus lens having a concave surface toward the image side; a second lens negative meniscus lens having a concave surface toward the image side; a third lens biconcave lens; and a fourth lens positive lens; the second lens group consisting of, in order from the object side to the image side: a 2A lens group having a positive refractive power; and a 2B lens group having a positive refractive power as a whole, consisting of a 2B-1 positive lens, a 2B-2 negative lens, and a 2B-3 positive lens; and Conditional Formulae (1), (2), and (3) below being satisfied, 15<vd1<35  (1) −4.3<vd2BL2−vd1<10  (2) 0<vd4−vd1<30  (3) wherein vd1 is the Abbe's number of the 1-1 negative meniscus lens, vd2BL2 is the Abbe's number of the 2B-2 negative lens, and vd4 is the Abbe's number of the 1-4 positive lens.
 2. An imaging lens as defined in claim 1, in which Conditional Formula (4) below is satisfied: −0.015<θgF1−θgF2BL2<0.04  (4) wherein θgF1 is the partial dispersion ratio of the 1-1 negative meniscus lens, and θgF2BL2 is the partial dispersion ratio of the 2B-2 negative lens.
 3. An imaging lens as defined in claim 2, in which Conditional Formula (4-1) below is satisfied: −0.013<θgF1−θgF2BL2<0.03  (4-1).
 4. An imaging lens as defined in claim 1, in which Conditional Formula (5) below is satisfied: 0<θgF1−θgF4<0.2  (5) wherein θgF1 is the partial dispersion ratio of the 1-1 negative meniscus lens, and θgF4 is the partial dispersion ratio of the 1-4 positive lens.
 5. An imaging lens as defined in claim 4, in which Conditional Formula (5-1) below is satisfied: 0.02<θgF1−θgF4<0.15  (5-1).
 6. An imaging lens as defined in claim 1, in which Conditional Formula (6) below is satisfied: −0.5<f/fL1<−0.2  (6) wherein f is the focal length of the entire lens system, and fL1 is the focal length of the 1-1 negative meniscus lens.
 7. An imaging lens as defined in claim 6, in which Conditional Formula (6-1) below is satisfied: −0.4<f/fL1<−0.25  (6-1).
 8. An imaging lens as defined in claim 1, in which Conditional Formula (7) below is satisfied: 0.5<f2B/f2A<2  (7) wherein f2B is the focal length of the 2B lens group, and f2A is the focal length of the 2A lens group.
 9. An imaging lens as defined in claim 8, in which Conditional Formula (7-1) below is satisfied: 0.7<f2B/f2A<1.6  (7-1).
 10. An imaging lens as defined in claim 1, in which Conditional Formula (8) below is satisfied: −30<(vd1+vd2BL2)/2−vd4<0  (8) wherein vd4 is the Abbe's number of the 1-4 positive lens.
 11. An imaging lens as defined in claim 10, in which Conditional Formula (8-1) below is satisfied: −25<(vd1+vd2BL2)/2−vd4<−5  (8-1).
 12. An imaging lens as defined in claim 1, in which Conditional Formula (9) below is satisfied: 0<(θgF1+θgF2BL2)/2−θgF4<0.2  (9) wherein θgF1 is the partial dispersion ratio of the 1-1 negative meniscus lens, θgF2BL2 is the partial dispersion ratio of the 2B-2 negative lens, and θgF4 is the partial dispersion ratio of the 1-4 positive lens.
 13. An imaging lens as defined in claim 12, in which Conditional Formula (9-1) below is satisfied: 0.02<(θgF1+θgF2BL2)/2−θgF4<0.15  (9-1).
 14. An imaging lens as defined in claim 1, wherein: the 2A lens group consists of, in order from the object side to the image side, a 2A-1 positive lens, a 2A-2 negative lens, and a 2A-3 positive lens.
 15. An imaging lens as defined in claim 14, wherein: the 2A-3 positive lens is a positive lens having a convex surface toward the image side; and the 2B-1 positive lens is a positive lens having a convex surface toward the object side.
 16. An imaging lens as defined in claim 1, in which Conditional Formula (1-1) below is satisfied: 16<vd1<32  (1-1).
 17. An imaging lens as defined in claim 1, in which Conditional Formula (2-1) below is satisfied: −3.8<vd2BL2−vd1<5  (2-1).
 18. An imaging lens as defined in claim 1, in which Conditional Formula (3-1) below is satisfied: 5<vd4−vd1<28  (3-1).
 19. An imaging apparatus equipped with an imaging lens as defined in claim
 1. 